A “converter for light sources” is an electrical circuit, which can be powered with an input voltage, and which can be connected to the light source, e.g. one or more LEDs, in order to thus be operated electrically in a defined manner.
WO 2014/060899 A2, by way of example, is known from the prior art, in which a converter for light sources is described in FIG. 1, which can serve as the starting point for the invention. A similar converter for light sources is also shown in FIG. 1 herein. A control circuit SE controls an inverter half bridge HB with two switches S1, S2 that are connected in series. As is illustrated in FIG. 1, the half bridge circuit HB is powered by an input voltage, which is depicted by way of example as a bus voltage VBus. Instead of a bus voltage, which is normally a DC voltage, i.e. a direct current voltage, a rectified alternating current voltage can also serve to power the half bridge.
Starting from a central point on the half bridge HB, or between the two switches S1, S2, respectively, a resonance circuit is then powered, formed in particular by a series connection of a capacitor C1, an inductor L1 and a second inductor L2a. Starting from the inductor L2a, a transformer T1 is then supplied with an alternating current voltage, i.e. an AC voltage. The transformer T1 contains the electromagnetic inductors, coils or windings L2a, L2b, L2c. The inductors L2b and L2c are disposed on the secondary side of the transformer T1. The inductors L2b and L2c are depicted as separate inductors, because a center tap is provided on the secondary side of the transformer T1.
Starting from the inductors L2b and L2c, a respective current path SP1 or SP2 is then powered. The current paths SP1 and SP2 thus each connect one side of the inductors L2b, L2c to a connecting point CP, wherein each current path has a diode for rectification.
The first current path SP1 has the diode D1, and the second current path SP2 has a second diode D2. An induced current ISP1 is conducted via the first current path SP1, and an induced current ISP2 is conducted via current path SP2. Moreover, an output connection E1 of the converter for light sources is connected to the connecting point CP, to which a load LED, e.g. a light source, and in particular at least one LED, can be connected.
Furthermore, a smoothing capacitor C2 is connected between the connecting point CP and the output connection E1 at its higher potential side, wherein the side of the second capacitor C2 with the lower potential can lie on the secondary side ground potential of the transformer.
The control circuit SE controls the higher potential switch S1 of the half bridge HB via a control signal HS (“high side” signal), and it controls the lower potential switch S2 of the half bridge with a signal LS (“low side” signal). The control circuit SE switches on the switches S1, S2, preferably configured as transistors, e.g. FET, MOSFET, in an alternating manner, in order to provide an alternating current voltage for the transformer Ti at the center of the half bridge HB.
In FIG. 1, the primary winding L2a of the transformer T1 is connected at its lower potential side to the primary side ground, as is likewise the case with the lower potential side of the half bridge switch S2. The current, or the voltage, flowing through the primary side inductor L2a is conducted through the transformer T1 to the secondary side, by means of which the current ISP1 is induced in the first current path SP1, and the current ISP2 is induced in the second current path SP2.
The center tap between the secondary side inductors L2b and L2c provides currents or voltages at the connecting point CP, which lie substantially symmetrically on either side of a zero point.
A direct current, or a direct current voltage, is provided at the connecting point CP via the diodes D1 and D2, in order to operate the load LED. The secondary side ground can either be connected to the primary side ground or it can be insulated therefrom.
On the whole, the voltage, or the current ISP1 or ISP2 at the output E1 depends on the voltage, or the waveform of the voltage, at the primary side inductor of the transformer T1. These can be adjusted by changing a timing or switching frequency of the switches S1, S2, or a duty cycle of the half bridge circuit HB, i.e. in particular through a change in the on-time of the switches S1, S2.
Starting from the circuit shown in FIG. 1, there is the problem that the inductances L2b, L2c on the secondary side of the transformer T1 (which represent, in particular, two halves of a single secondary side inductor) are not precisely symmetrical, and do not have the same electrical or symmetrical parameters. This leads to an asymmetrical load to the downstream components on the secondary side of the transformer T1, and in particular the diodes D1 and D2. As a result, it is possible that only one of the current paths SP1, SP2, and thus one diodes D1/D2, is charged.